Sign-tolerant HTTP/1 chunk-size parser in Mint enables response smuggling against strict intermediaries on pooled connections

{
  "id": "34a934896b2b840d54191b50ea4f7752b0eac8c76d993ba29310105144e0c2f5",
  "url": "https://osv.dev/vulnerability/CVE-2026-59249",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Sign-tolerant HTTP/1 chunk-size parser in Mint enables response smuggling against strict intermediaries on pooled connections",
    "summary": "Inconsistent interpretation of HTTP requests (HTTP response smuggling) vulnerability in elixir-mint mint allows a malicious HTTP/1 server to desynchronize a strict intermediary and the Mint client on the same pooled connection, enabling response-queue poisoning against subsequent requests that share the connection. The Mint.HTTP1.decode_body/5 function in lib/mint/http1.ex parses the chunk-size line of a Transfer-Encoding: chunked response with Integer.parse(data, 16). RFC 7230 defines chunk-size = 1*HEXDIG and forbids any sign prefix, but Integer.parse/2 accepts an optional leading + or -. A chunk-size line of +5 is accepted as a five-byte chunk; lines of +0 and -0 are accepted as the terminating zero-length chunk and end the message body early. An RFC-strict intermediary in the response path rejects these forms, so the intermediary and the Mint client disagree on where one response ends and the next begins. On a pooled keep-alive connection, an attacker-influenced origin can inject bytes that the client attributes to the next legitimate response on the same connection, poisoning the response queue and corrupting the responses returned to unrelated in-flight requests. This issue affects mint: from 0.1.0 before 1.9.3.",
    "evidence": "osv:CVE-2026-59249",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-59249",
      "aliases": [
        "CVE-2026-59249",
        "EEF-CVE-2026-59249",
        "GHSA-x3x7-96vm-6h2w"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/elixir-mint/mint",
              "type": "GIT",
              "events": [
                {
                  "introduced": "60089586ec7adc9fddb09f69a2f5919ba9ac7f33"
                },
                {
                  "fixed": "fc7d16538db7e40b56ed489f08683225cb0197fa"
                },
                {
                  "introduced": "47889857fb36f07606ad9c2e52080d202d419058"
                },
                {
                  "fixed": "f0b72c0b2363c98d0a220019d108ac6141715428"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "60089586ec7adc9fddb09f69a2f5919ba9ac7f33"
                      },
                      {
                        "fixed": "fc7d16538db7e40b56ed489f08683225cb0197fa"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0.1.0"
                      },
                      {
                        "fixed": "1.9.3"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "fixed": "fc7d16538db7e40b56ed489f08683225cb0197fa"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.9.2",
            "v1.9.1",
            "v1.9.0",
            "v1.8.0",
            "v1.7.1",
            "v1.7.0",
            "v1.6.2",
            "v1.6.1",
            "v1.6.0",
            "v1.5.2",
            "v1.5.1",
            "v1.5.0",
            "v1.4.2",
            "v1.4.1",
            "v1.4.0",
            "v1.3.0",
            "v1.2.1",
            "v1.2.0",
            "v1.1.0",
            "v1.0.0",
            "v0.5.0",
            "v0.4.0",
            "v0.2.1",
            "v0.2.0",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-59249.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:35.738632822Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-59249.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-59249",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59249.json",
        "https://github.com/elixir-mint/mint/security/advisories/GHSA-x3x7-96vm-6h2w",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-59249",
        "https://github.com/elixir-mint/mint/commit/fc7d16538db7e40b56ed489f08683225cb0197fa",
        "https://github.com/elixir-mint/mint"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-444"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59249.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-59249",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 503075,
  "published_at": "2026-07-16T11:39:29.939+00:00"
}